There are two primary types of corn processing conducted presently: dry grind and wet milling processes. The wet milling processes are efficient in their use of corn since they produce numerous high value corn products, such as corn oil, starch, corn gluten meal, corn gluten feed, and corn steep liquor. However, the wet milling processes require very high capital investments in machinery. Dry grind processes are used to produce ethanol and animal feed. Animal feed is substantially less valuable than corn oil and zein, which are left in the animal feed produced by a dry mill process. A reason for existence of the dry grind plants to date has been government ethanol subsidies, which are likely to disappear.
Some methods to extract oil and zein from dry mill corn have been proposed in the literature, but have yet to demonstrate efficiency meeting commercial production requirements. One type of proposed method is embodied in U.S. Pat. No. 4,716,218 and a “Sequential Extraction Process” developed at Iowa State University. This type of method uses ethanol to extract oil and zein. Evaporation is required to remove the ethanol, and then hexane-extraction is used to separate the oil from the zein with further subsequent evaporation of the hexane from the oil. These are relatively complicated processes. They are also expensive due to their energy intensive nature. Significant heating requirements result from the multiple required evaporations. Further, the evaporations create pollution concerns.
Another proposed method to remove oil from dry-milled corn is mechanical degermination. This method produces corn germ with less than approximately 50 percent oil. The germ must be subsequently processed to recover the oil. No ability to recover zein is presented by this method, however, and there is no known utilization of the method to obtain corn oil and zein in a manufacture scaled product.
Thus, there is a need for an improved method capable of using dry grind corn, as well as wet milled corn product, to produce one or more corn products of value. It is an object of the invention to provide such a method. It is a further object of the invention to provide a method for extracting corn oil and/or protein (particularly zein), which method is capable of utilizing dry grind corn or wet milled corn product through ethanol treatment with filtration.